Reinforcement of natural rubber using a novel combination of conventional and in situ generated fillers

Abstract

Carbon black (CB) is the most widespread reinforcing filler found in rubber compounds. However, the need to reduce its use due to the environmental consequences of its production has led to the incorporation of other fillers such as precipitated silica (p-Si), although latter does not provide an equivalent reinforcement owing to its inherent incompatibility and difficulties during mixing. The sol-gel method stands up as a non-conventional technique to overcome these issues. This methodology enables the incorporation of fillers in situ. By this means, compatibility is improved, and superior reinforcement is achieved because of better dispersion and smaller particle size. In this work, natural rubber (NR) composites with conventional fillers (CB and p-Si), non-conventional (in situ silica, i-Si and in situ zirconia, i-Zi) and novel combinations among them were prepared by merging standard mechanical mixing and the sol-gel method, and systematically characterized. The compound in which CB is combined with i-Si presents the best overall performance with a higher mechanical strength at low (100%) and medium (300%) deformations, a tear resistance of (70 ± 5) kN/m and an abrasion resistance of (156 ± 9)% (considerably higher values than the pure NR and the formulations with the separate fillers). The methodology here presented facilitates the incorporation of nanofiller precursors into a vulcanized elastomeric matrix in a post-processing stage; hence, this approach can be considered in the near future as an effective way to reinforce already discarded or recycled rubbers, including end-of-life tires.

Keywords

• Natural rubber
• Carbon black
• Silica
• Zirconia
• Nanocomposites
• Sol-gel method